Precise Synthesis of High Generation Dendrimer-Like Star-Branched Polymers and Their Applications

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Dendrimer-like star-branched polymers have been synthesized by developing a novel methodology which involves two basic reactions: (1) linking reaction of α-functionalized living anionic polymers with benzyl bromide-functionalized polymers and (2) transformation reaction to benzyl bromides. The two reactions proceeded quantitatively several times, resulting in the formation of high-generation dendrimer-like star-branched polymers up to seventh generation. The resulting polymer (7th generation) is a really huge macromolecule possessing two million in molecular weight and a narrow molecular weight distribution (Mw/Mn =1.02) and comprising 508 polymer segments with 512 termini. Highly dense polymers consisting of four branches at each junction have also succeeded in synthesizing the polymers up to the third generation. The attempt to synthesize the 4th generation polymer was not successful possibly due to the steric hindrance. Other functional polymer segments have been successfully introduced into the outermost layers of dendrimer-like star-branched polymers. They involve poly(2-vinylpyridine), poly(tert-butyl methacrylate), poly(3-perfluorobutylpropyl methacrylate), and poly(2,3-dihydroxypropyl methacrylate), respectively. By introducing such segments, basic, acidic, ionic, hydrophobic and lipophobic, water-soluble characters could be provided to the polymers. Furthermore, the introduction of methacrylate polymers having liquid crystalline, chirality, and thermoresponsive characters were also successful. Their functional polymers have been examined in detail with respect to such functionalities. The shapes of the dendrimer-like star-branched polymers have been measured by SAXS and found to be ellipsoidal shapes rather than spherical ones. AFM structural imaging of the dendrimer-like star-branched polymers has been realized. The structures based on synthetic methodology as well as internal branching points could be clearly observed for the first time.